In the testing of samples, it is necessary normally to deliver a specified volume of a sample into a test apparatus so that the quantitative data obtained from the test apparatus is meaningful. Where the source of the specimen is generous, it is of no major consequence that some portion of the sample is spilled or otherwise wasted. Some wastage is desirable because this helps assure that the test apparatus has a full sized, metered specimen input to it. By way of contrast however, many chemicals exist in such minute quantities that it is foolish to waste any of the sample. As an example, sophisticated medical research involving test animals which are relatively small may create a specimen which is distinctly small. For instance, in the investigation of hormonal problems in small test animals such as rabbits or guinea pigs, or in other problems too numerous to exemplify, the material obtained for testing may be extremely small and minute. Accordingly, there is not enough of the material to fill a standard sample loop. Sample loops are normally installed with sample injection valves connected at the input of a chromatographic test device. A sample loop will typically hold from about 10 microliters to 10 milliliters of a sample. When the sample available is smaller than the precise volume of the loop, difficulties arise in the delivery of the sample from some sort of source or carrier into the sample injection valve.
Sample injection syringes have been used heretofore. They have met with some success. However, they have been limited in that it is difficult to transfer a small sample (smaller than the standard loop available) into the loop. The apparatus of the present invention has overcome this problem. This apparatus has overcome the problem by taking into account the offset error which would occur upon using a conventionally configured syringe to inject into a sample injection valve.
The sample injection valves are normally manufactured with a rotatable plug in the valve body, there being a number of ports or passages in the valve body which deliver the specimen into the sample loop. The sample loop is normally connected between two specified ports of the valve. When the measured specimen is delivered through an inlet port and flows through passages in the sample injection valve, a portion of it ends up in certain connecting spaces between the inlet port and the sample loops. When the plug is rotated, a portion of the sample is not transferred.
It has been discovered that a sample injection syringe having a set of offset calibrations which has an offset equal to the volume between the end of the syringe needle or inlet tube and the front of the sample in the valve (having the form of connecting space) is advantageously used. As a consequence, the apparatus of the present invention is able to deliver a sample which differs from the size of the standard sample loop. Nevertheless, the sample is delivered into the loop and is precisely known or measured by the sample injection syringe. Moreover, the offset which occurs in the operation of the valve is overcome so that the metered quality of sample delivered into the sample loop is controlled.